This invention relates generally to valves and more particularly to directional control valves for pneumatic applications.
Spool valves are used and known in the art as directional control valves for changing the direction of a motive fluid to and from pistons or diaphragms located within cylinders or other chambers, respectively. A conventional spool valve comprises a valve body and a sliding spool actuator which, upon shifting therein, alternately defines flow passages within the valve body to a supply pressure or an exhaust port causing a cylinder's piston rod or chamber's diaphragm to be moved and work performed.
Typically, such directional control valves have been used as the major distribution valve for providing a pressurized motive fluid, e.g., pressurized air, to chambers associated with a double acting diaphragm pump. Examples are shown in commonly assigned U.S. Pat. Nos. 4,854,832, 5,391,060, and 6,722,256, the disclosures of which are incorporated herein by reference. In U.S. Pat. No. 5,391,060, a spool valve is disposed in a valve body and connects air supply and exhaust ports to appropriate diaphragm air chambers via O-rings located on the spool valve. U.S. Pat. Nos. 4,854,832 and 6,722,256, include a spool valve having a spool actuator that has “U”-cup seals and receives a sliding “D” valve that establishes fluid interconnections upon shifting of the spool valve. As shown in the aforementioned patents, preferably, the spool actuators are differential actuators having at least two diameters to respond to a differential pressure in order to prevent stalling of the valve.
The seals used on such spool actuators such as the “O”-ring and “U”-cup seals described above, however, require excellent inner surface finishes on the valve body bores. To prolong seal life, a lubricant is also generally used either in the bore or in the seal itself to help reduce friction in moving the piston. However, many pumping applications require a lubrication-free environment to avoid contamination of the media being handled.
The foregoing illustrates limitations known to exist in present valving devices. Thus it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly an alternative valving apparatus is provided including the features more fully disclosed hereinafter.